No Brakes on a Rocket

With every kind of transport we use, making it move is only one part of the problem. The other, which is equally important, is to be able to slow down its movement and to stop it.

Land vehicles are fitted with brakes, which usually work by causing friction on the wheels or other moving parts. We can stop a toboggan by applying the friction to the ground with our feet.

With no air or water, and no ground anywhere near it, the rocket cannot be slowed down by any kind of friction. Out in space, once it is moving, it will continue to move until something else either pushes against it or pulls it back. This is why it is important that the rocket is sent on its right course to begin with. A small error at the beginning could cause a very big one later on.

It is possible, however, to control the rocket after launching it into space, by using forward-pointing jets of gas like those which can be used to steer it. Far into space, where the pull of the earth's gravity is weakened, only a small push is needed to reduce speed, and one way of applying the push backwards, is by using containers of compressed gas which can be released a little at a time.

These backward-firing jets are sometimes called 'retro-rockets', and without them it would be impossible to slow down the rocket once it had been sent on its course.